ILWS WORKSHOP 2006, GOA, FEBRUARY 19-20, 2006
The Atmosphere-Space Interactions Monitor (ASIM) for the
International Space Station
T. Neubert1, I. Kuvvetli1, C. Budtz-Jørgensen1, N. Østgaard2, V. Reglero3 and N. Arnold4
1
Danish National Space Center, Copenhagen Denmark, [email protected]
University of Bergen, Norway
3
Universidad de Valencia, Spain
4
University of Leicester, UK
2
Abstract. The Atmosphere-Space Interactions Monitor (ASIM) is an instrument suite to be mounted on an external platforms
on the International Space Station (ISS). ASIM will study the coupling of thunderstorms processes to the upper atmosphere,
ionosphere and radiation belts and energetic space particle precipitation effects in the mesosphere and thermosphere. The
scientific objectives include (1) investigations into sprites, jets, elves and relativistic electron beams injected into the
magnetosphere above thunderstorms, (2) studies of gravity waves in the thermosphere above severe thunderstorms, (3)
lightning-induced precipitation of radiation belt electrons, (4) auroral electron energetics, and (5) ozone and NOx
concentrations in the upper atmosphere. The instruments are 4 TV frame-rate, narrow-band, optical cameras and 4 photometers
viewing towards the limb, and an X-ray sensor, 2 cameras and 2 photometers viewing towards the nadir. ASIM is currently in
Phase A.
Index Terms: 0310 Airglow and Aurora; 2455 Particle precipitation; 3304 Atmospheric electricity; 3332Mesospheric
dynamics
_____________________________________________________________________________________________________
1. Introduction
The mesosphere and lower thermosphere are the regions of
the atmosphere about which the least is known. They are too
low for in situ spacecraft observations, too high for balloon
observations, and remote sensing is hampered by low
densities and a high degree of variability over a range of time
and spatial scales. As a consequence, these regions have
received less attention than more readily accessible regions
above and below. In many respects, the mesosphere and
lower thermosphere represent an uncharted “frontier” for
upper atmospheric science.
The Atmosphere-Space
Interactions Monitor (ASIM) will study the interaction of
thunderstorms with the upper regions of the atmosphere –
reaching into the ionosphere and magnetosphere and
energetic space particle radiation effects on the thermosphere
and mesosphere.
Thunderstorm-driven processes studied include the newly
discovered Transient Luminous Emissions (TLES). The most
commonly observed from ground is the “sprite”, a
manifestation of electrical break-down in the mesosphere.
Other classes include the “blue jet”, a discharge propagating
upwards into the stratosphere from cloud tops, and the
“elve”, a concentric ring of emissions from neutrals excited
by a lightning EMP at the bottom edge of ionosphere.
Observations have further documented giant discharges
creating electrical breakdown of the atmosphere from the top
of thunderstorms to the bottom ionosphere (Pasko et al.,
2002; Su et al., 2003). The pantheon of the most commonly
observed emissions of the upper atmosphere, also referred to
as “Transient Luminous Events” (TLEs), is shown in Fig. 1.
Fig. 1. The anatomy of upper atmospheric flashes (Neubert, 2003).
Within the past decade, a different, but possibly related,
type of flashes has been discovered. These are the Terrestrial
Gamma-ray Flashes (TGFs) from the atmosphere above
thunderstorms, first recorded from the Compton Gamma Ray
Observatory (CGRO) satellite (Nemiroff et al., 1997). TGFs
are of a few msec-duration with energies from ~100 keV to
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Neubert et al: The Atmosphere-Space Interactions Monitor (ASIM) for the International Space Station
beyond 1 MeV. More recent observations are now available
from the Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) satellite launched in 2002, which is detecting 10 to
20 TGFs per month with energies up to 20 MeV. This rate of
observations is much higher than CGRO (75TGFs/9years)
because of a better instrument sensitivity. It suggests an
average global TGF rate of ~50 per 24 hours (Smith et al.,
2005). The distribution of events over a 2-month period
(satellite ground track position) is shown in Fig. 2 on top of a
color coded representation of the average global lightning
activity. The distribution is correlated with thunderstorm
activity except over the Americas.
holds the additional promise of improving our knowledge of
the regions in which they occur – the mesosphere – the least
known region of the atmosphere.
2. ASIM scientific objectives
The goal of the missions is to advance our understanding of
electrical- and energetic charged particle effects on the
stratosphere, mesosphere, and lower thermosphere. The
Research Objectives (RO) of the mission are given below.
Primary objectives based on observations:
RO1:
RO2:
RO3:
RO4:
Fig. 2. RHESSI observations of TGFs..(Smith, personal communication).
The run-away electron discharge is suggested in lightning,
sprites and TGFs (Roussel-Dupré and Gurevich, 1996;
Gurevich et al., 1999). Evidence for the process builds on Xand
γ-rays
associated
with
thunderstorm
charging/discharging measured from balloons, mountain
tops, and in rocket-induced lightning (Parks et al., 1981;
McCarthy et al., 1985; Eack et al., 1996; Dwyer et al.,
2004a,b; 2005). Simulations of sprites indicate that 106-107
electrons/cm2, accelerated in the ~100 MV potential between
cloud tops and the ionosphere following a lightning
discharge, are injected into the magnetosphere (Lehtinen et
al., 1997). Thunderstorms also provide a sink of radiation
belt electrons. It is well known, that lightning produced
whistler waves may scatter energetic electrons into the losscone (Voss et al., 1998). LEPs and sprites are observed in
perturbations of ground transmitter signals induced by patchy
changes in plasma densities of the lower ionosphere
(Haldoupis et al., 2002).
Sparked by the discovery of TLEs and TGFs, our
understanding of fundamental processes related to
atmospheric electricity and energetic charged particle effects
are under re-evaluation (Arnold and Neubert, 2002). It is now
understood that thunderstorms of the troposphere couple to
the stratosphere, mesosphere and the near-earth space
through electric fields, energetic charged articles, and gravity
waves, and that precipitating charged particles from space,
such as auroral and radiation belt particles and cosmic rays,
couple to the atmosphere. The current research efforts into
the perturbation of the atmosphere induced by these
processes further support the view, also put forward in other
areas of atmospheric research, that global models of
atmospheric chemistry and circulation, for proper
representation of the dynamics, must include all atmospheric
layers reaching from the surface to the ionosphere. An indepth understanding of the newly discovered TLEs and TGFs
RO5:
RO6:
A comprehensive global survey (lat, UT, season) of
TLEs and TGFs rates.
Study the physics of TGFs and their relationship
with TLEs and thunderstorms.
Study the physics of TLEs.
Determine
the
characteristics
that
make
thunderstorms TLE- and TGF-active.
Study the coupling to the mesosphere, thermosphere
and ionosphere of thunderstorms and TLEs.
Study the effects of thunderstorms and TGFs on the
Earth’s radiation belts
Primary objectives based on modeling:
RO7:
RO8:
RO9:
Quantify chemical effects of TLEs, TGFs and
energetic particle precipitation on the stratosphere,
mesosphere, and lower thermosphere
Quantify effects of TLEs and TGFs on the
atmospheric electric circuit
Quantify perturbations to atmospheric dynamics
from thunderstorms, TLEs, TGFs, and energetic
particle precipitation
Secondary objectives based on observations:
RO10: Spectroscopic studies of the Aurora
RO11: Studies of greenhouse gas concentrations above
thunderstorms (NOx, O3)
RO12: Studies of meteor ablation in the mesosphere and
thermosphere
RO 1-6 establish the foundation for answering questions
relating to the basic physics of TLEs and TGFs and their
global occurrence rates as a function of season and local
time. This information is needed in order to estimate
perturbations to the chemical and electrical properties of the
atmosphere induced by the emissions contained in RO 7-8.
The estimates are based on models of the global electric
circuit to be refined during the project, and on chemical
models of effects from energetic particle precipitation from
space primarily at high latitudes adapted for the study of
TLEs and TGFs. Both electrical and chemical properties may
affect the radiation properties and thus the dynamics of the
atmosphere. This aspect as studied in RO 9 by means of local
and global modeling of the atmosphere.
ILWS WORKSHOP 2006, GOA, FEBRUARY 19-20, 2006
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3. ASIM mission scientific requirements
The primary research objectives of the mission require the
following measurements:
RQ1:
RQ2:
RQ3:
RQ4:
Optical detection of TLEs with high spatial- and
time resolution in selected spectral bands (detailed
below). The requirement is met by optical imaging
cameras with the required spatial resolution and
photometers with the required time resolution. The
instruments must view towards the Limb.
X- and γ-ray detection of TGFs with high time
resolution and at photon energies reaching down to
10keV (detailed below). The requirement is met by
a detector with the required sensitivity and time
resolution. Viewing must be towards the Nadir in
order to minimize atmospheric absorption.
Simultaneous optical detection of thunderstorm- and
TLE activity with TGF activity. The optical
instruments must view with the X- and γ-ray
detector towards the Nadir.
Observations from space during minimum one year
at all local times to observe seasonal and local time
variations in thunderstorm-, TLE-, and TGF activity.
The optical instruments make up the Miniature Multi-spectral
Imaging Array (MMIA) of 3 modules each housing 2 videorate cameras and two photometers. Two modules view in the
ram-direction towards the limb and one module towards the
nadir. A Miniature X- and Gamma-Ray sensor (MXGS) view
towards the nadir.
The bands of interest for optical observations are shown in
Table 1. The electron energy shown (band 1, 2, 4) is the
minimum energy of the free electrons sampled by the
selected band. Band 1 and 2 are selected because they are
relatively simple to interpret in terms of electron energetics
and ionization, but difficult to observe from ground because
of UV absorption in the atmosphere. Band 4 covers the
spectral range of maximum sprite emission rate. Band 3 is
one of the brightest airglow emission lines and comes from a
layer around 90 - 100km altitude. Their intensity is
modulated by gravity waves. The limb-viewing geometry is
best for TLE observations, while the nadir module is needed
to correlate lightning and TLE activity with MXGS
observations of TGFs. The optical bands are well known in
auroral research. Thus ASIM provides an opportunity to
observe aurora during magnetic storms when the auroral oval
extends to low latitudes covered by the ISS (51.6o
inclination). The aurora is first seen by the Limb instruments
pointing in the ram-direction – then during overflight by the
nadir instruments.
Table 1. Optical bands for cameras and photometers. The Limbinstrument point towards the ram-direction.
#
1
2
3
4
B/ ΔB (nm)
337/10
391/5
762/5
650..800
Transition
N2(2P)
N2+(1N)
O2(0,0)
N2(1P)
Process
11.1eV
18.5eV
Grav.w.
7.5eV
Pointing
Limb, Nadir
Limb
Limb
Limb, Nadir
Instrument
Cam/Phot
Cam/Phot
Cam
Cam/Phot
TBD
TBD
NOx
Limb
Phot
Further specifications of the optical instruments are shown in
Table 2.
Table 2: Optical instrument specifications.
Cameras
Limb
Nadir
Photom
Limb
Nadir
FOV
[deg]
20
80
Lens
[mm]
50
11
20
80
TBD
TBD
Pixels
XY
1000
1000
Pixel-res
[km]
0.6-0.8
0.7
Frame-rate
[Hz]
25
25
Sample-rate
[kHz]
10
10
The MXGS instrument is a ~550 cm2 detector of CdZnTe
crystals sampling the energy range ~10-500keV. The energy
range is chosen to sample the range affected by atmospheric
absorption and thus sensitive to the altitude of TGF
generation. This range is also well suited to study auroral
processes and lightning-induced electron precipitation.
The ASIM instruments are baselined for the external
platforms of the European Space Agency (ESA) laboratory
module, Columbus. The module is scheduled for launch in
2007 and ASIM is scheduled for 2009. Should shuttle
launches not be available for ASIM, the modular design of
the payload will allow for a launch on the European
Automated Transfer Vehicle (ATV) or the Russian Progress.
Likewise, ASIM can be adapted to the Russian (or other)
external platforms available on the ISS. Fig. 3 shows the
ASIM instruments on the adaptor plate used for the
Columbus module.
Fig. 3. The ASIM payload.
4. ASIM for the ILWS Programme
The secondary science objectives are met by the instruments
required for the primary science objectives. Optical and x-ray
measurements are used to study aurora, differential
absorption of light emissions from lightning-illuminated
thunderstorm clouds measured by photometers defines ozone
column densities, NOx production in TLEs is to be
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Neubert et al: The Atmosphere-Space Interactions Monitor (ASIM) for the International Space Station
monitored by photometer 5, and optical imaging and
photometers will be used to study meteor ablation.
Of primary interest to the ILWS programme are the auroral
studies. The measurements include imaging in 4 auroral
bands simultaneously, coupled with high time-resolution
photometer observations and X- and γ-ray observations. The
inclination of the ISS orbit at 51.6o brings the instruments
over the auroral oval during periods of high solar
(geomagnetic) activity when the auroral oval expands to
lower latitudes. These are also periods with high auroral
activity. The aurora is first seen towards the limb in the ramdirection (the direction of the ISS velocity vector) in 4 optical
bands and then in the nadir direction in to optical bands and
in the x- and gamma-ray band as the ISS passes over the
aurora. Fig. 4 shows the aurora from the space shuttle in the
limb-viewing geometry.
Fig 4. The aurora seen from the space shuttle (Hallinan).
Of particular interest are passes over Canada, where the
auroral region extends to relatively low geographic latitudes
due to the 11.4o shift in latitude towards Canada of the
geomagnetic pole relative to the geographic pole. Canada is
in the process of extending their ground network of optical
all-sky auroral cameras and magnetic stations. The
combination of space and ground observations provides for a
powerful tool for studying auroral processes and their
dependence on solar and space activity.
The ASIM mission can be an important component of the
International Living With a Star (ILWS) programme. It
would in particular complement the Canadian-Chinese
KuaFu-B dual satellite mission (formerly Ravens), the
radiation belt mappers of NASA, and the SWARM mission
of ESA.
Acknowledgments. One of the authors would like to thank the
wider ASIM team and in the international science team for
their dedication to the project.
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